In a hydraulic system, valves used to control the flow direction of fluids are generally called directional control valves.According to the use of valves and reversing valve.

① Check valve: Only allow the fluid in the pipeline one-way connection, the reverse is cut off. ② reversing valve: Changing the pass and break relationship between different pipelines, according to the valve core in the valve body of the number of work position of two bits, three-digit, etc. according to the control of the number of channels, two, three, four, five, etc., such as two two-pass, three-bit three-way, three-digit five-pass in accordance with the spool-driven mode of separation, mobile, electromagnetic, liquid and so on.